A new method to predict delamination in electronic packages

Interfacial delamination, due to the presence of dissimilar material systems, is one of the primary concerns in electronic package design. The mismatch in coefficient of thermal expansion between the different layers in the packages can generate high interfacial stresses due to thermal loading during fabrication and assembly. The present study is focused on the delamination at the epoxy molding compound (EMC)/copper interface. Different EMC materials molded on copper leadframe were tested with different shear height. The stresses at the interface were evaluated using data from the button shear test (BST). Conventional failure criteria are not able to explain the stress results observed from the button shear test data. In this study, a multi-scale model was built to determine the interfacial energy between EMC and copper substrate. The interfacial material properties were evaluated from the interaction energy between EMC and Cu substrate. The interaction of EMC and Cu can be measured using the atomic force microscope (AFM). The force-distance curve obtained directly from AFM measurement is used to determine the interfacial material properties. The properties were input to the multi-scale model. Experimental force from the BST was applied to the model. The interfacial tensile stress and shear stress were evaluated and were used to calculate the interfacial energy. An energy-based failure criterion for delamination was set up. In order to benchmark the delamination failure criterion, two electronic packages, SOT #1 and SOT #2 were studied to investigate delamination in the soldering reflow process. Based on the proposed method, the predicted results were found to be consistent with those from C-SAM measurement.